Which of the Lewis electron dot representations is correct for perchlorate, [tex]$ClO _4^{-}$[/tex]?
Answer (2)
Calculate the total valence electrons: 7 + 4 ( 6 ) + 1 = 32 .
Form single bonds between Cl and each O, using 8 electrons.
Distribute the remaining 24 electrons to the O atoms as lone pairs.
The correct Lewis structure has single bonds, with a +3 formal charge on Cl and -1 on each O.
T h e correc t L e w i s s t r u c t u re ha s s in g l e b o n d s b e tw ee n Cl an d e a c h O , w i t h 3 l o n e p ai rs o n e a c h O .
Explanation
Understanding the Problem We want to determine the correct Lewis structure for the perchlorate ion, Cl O 4 − . This involves understanding valence electrons, the octet rule, and formal charges.
Calculating Valence Electrons First, let's calculate the total number of valence electrons. Chlorine (Cl) has 7 valence electrons, and each oxygen (O) has 6. Since there are four oxygen atoms and an overall charge of -1, the total number of valence electrons is: 7 + 4 ( 6 ) + 1 = 7 + 24 + 1 = 32
Forming Single Bonds Now, let's consider a skeletal structure with chlorine as the central atom bonded to the four oxygen atoms. Each single bond represents 2 electrons. So, four single bonds use 8 electrons. We have 32 valence electrons in total, so we have 32 − 8 = 24 electrons remaining to distribute.
Completing Oxygen Octets We distribute the remaining 24 electrons to the oxygen atoms as lone pairs to satisfy the octet rule. Each oxygen atom needs 6 more electrons (3 lone pairs) to complete its octet. So, 4 o x y g e n a t o m s × 6 e l ec t ro n s = 24 electrons. This uses all the remaining electrons.
Calculating Formal Charges Now, let's calculate the formal charges. Formal charge is calculated as: F or ma l C ha r g e = ( Va l e n ce El ec t ro n s ) − ( N o n − b o n d in g El ec t ro n s ) − ( 2 1 B o n d in g El ec t ro n s ) For chlorine: F or ma l C ha r g e = 7 − 0 − ( 2 1 × 8 ) = 7 − 4 = + 3 For each oxygen: F or ma l C ha r g e = 6 − 6 − ( 2 1 × 2 ) = 6 − 6 − 1 = − 1
Minimizing Formal Charges To minimize the formal charges, we can form double bonds between the chlorine atom and some of the oxygen atoms. If we form one double bond, one oxygen will have a formal charge of 0, and the chlorine will have a formal charge of +2. If we form two double bonds, two oxygens will have a formal charge of 0, and the chlorine will have a formal charge of +1. If we form three double bonds, three oxygens will have a formal charge of 0, and the chlorine will have a formal charge of 0, and one oxygen will have a formal charge of -1. If we form four double bonds, all four oxygens will have a formal charge of 0, and the chlorine will have a formal charge of -1. However, chlorine can have an expanded octet, so it can accommodate more than 8 electrons. However, the best Lewis structure is the one with single bonds only, as it minimizes formal charges while still being a valid structure. The formal charges are +3 on Cl and -1 on each O. While these are not all zero, this structure is preferred over ones with double bonds because it better reflects the actual charge distribution in the perchlorate ion.
Final Lewis Structure Therefore, the correct Lewis structure for perchlorate, Cl O 4 − , has single bonds between the chlorine atom and each of the four oxygen atoms. Each oxygen atom has three lone pairs, and the chlorine atom has no lone pairs. The formal charge on chlorine is +3, and the formal charge on each oxygen is -1.
Examples
Understanding Lewis structures is crucial in chemistry for predicting molecular shapes and reactivity. For example, knowing the Lewis structure of perchlorate helps predict its behavior in reactions, such as its role as an oxidizing agent. In environmental science, understanding the structure and properties of ions like perchlorate is important for developing methods to remove them from contaminated water sources, ensuring safer drinking water. Lewis structures provide a foundation for understanding chemical bonding and molecular properties, which are essential in various scientific fields.
The Lewis structure for perchlorate Cl O 4 − includes chlorine bonded to four oxygen atoms via single bonds, with each oxygen atom holding three lone pairs of electrons. Chlorine has a formal charge of +3 and each oxygen has a formal charge of -1. This structure illustrates the electron distribution within the ion and is critical for understanding its chemical behavior.
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